[AlwaysQuestioning]

Hi guys. I'm a bit confused about these type of reactions. For example, for halogens, it takes both of the halogens to be in aqueous solutions for the reaction to occur. Secondly, for metal displacement reactions, aluminum powder can displace iron from its oxide when both are solids (does the heat play a part.)? And why doesn't the hydrogen ion in nitric acid for example, displace the anion from an insoluble salt that has been placed in it (e.g AgCl)?

Does the state at which these substances are in affect whether these displacement reactions can happen or not? And does heat affect whether or not they can happen? (for the metal example i stated)

Thanks so much.

[magician4]

For example, for halogens, it takes both of the halogens to be in aqueous solutions for the reaction to occur. (...)

no, it doesn't
with radicals involved, it can happen in every state, might it be liquid, solid or gas phase.
with ions, gas phase is most difficult (as ions are next to impossible to have there), but it also can happen in solid state, just so that it might take much much longer (as mobility is drastically reduced here)

for metal displacement reactions, aluminum powder can displace iron from its oxide when both are solids (does the heat play a part.)?

again, same picture
however, as I mentioned that solid state reactions take their time, this very much is true for termite reaction, too.
In fact, in solid state it is that pretty slow, that you can store readily mixed termite for a lifetime, without anything major happening.
If you were in for a faster rate of reaction, you'd try to liquefy situation at least. That's what the magnesium fuse is all about, i.e. that's where "heat" comes into play...

And why doesn't the hydrogen ion in nitric acid for example, displace the anion from an insoluble salt that has been placed in it (e.g AgCl)?

because, without the help of additional bonds, the combination  of two even charged particles , i.e. H⁺/Ag⁺ in this case, doesn't make for stable molecules normally


regards

Ingo

[AlwaysQuestioning]

What i meant is displaced the cation (the silver ion) from AgCl.... Sorry bout that 

[magician4]

What i meant is displaced the cation (the silver ion) from AgCl.... Sorry bout that

speaking from a strictly thermodynamical point of view: you're wrong here, too

of course it will: AgCl(s) + HNO_{3(diss., aq.)}  <--(water)--> Ag⁺_aq. + HCl_{(diss., aq.)} + NO₃^-_(aq)

only: simply to a very very very low extend at that, just enough to reach thermodynamical equilibrium for the system, with respect to all chemical potentials involved here. hence, the equilibrium is strongly leftsided.
... as the formation of insoluble AgCl is a very powerful driver here, speaking from the aspect of "the energy gained for the system", with the precipitation of this solid

that's why (mostly...there's a million of minor reasons of second order, of course...)

regards

Ingo

[AlwaysQuestioning]

Thanks so much!!!!!!!!